1. Field of the Invention
The present invention relates to a transporter to carry very heavy loads. More particularly, the present invention relates to a transporter with single wheel power driven axle assemblies that have omni-directional steering, fluid equalizing suspension, and on-center axle rotation capability in order to carry very heavy loads.
2. Description of the Related Art
A nuclear reactor operates by facilitating a controlled nuclear chain reaction in a reactor core. Typically, the nuclear reaction is fueled by an isotope of uranium, which is supplied to the reactor core in a plurality of elongated fuel rods, which are typically metallic structures that are packed with uranium pellets.
When the fuel rods must be removed and replaced, the spent nuclear fuel is typically temporarily stored in water pools that dissipate generated thermal energy and attenuates radiation emitted from the spent nuclear fuel. For long-term storage, the spent fuel rods are transferred to either horizontal or vertical radiation shielded and ventilated concrete casks. The present invention deals with vertical-type cask systems. These casks used to store the spent nuclear fuel are vertical-standing, cylindrical, radiation-sealing concrete casks typically weighing at least 150 to 200 tons. Once the spent nuclear fuel is in a cask, the cask needs to be transported from the nuclear refueling facility to an Independent Spent Fuel Storage Installation (ISFSI). The ISFSI is designed for the long term storage of decaying radioactive materials.
Various options exist for transporting vertical-type casks both within a nuclear refueling facility and from a nuclear refueling facility to an ISFSI. These options include heavy multi axle specialized carrier trailers, industrial air cushion devices (so called “air bearings”), overhead cranes, and specialized vertical lift gantry frames attached to a crawler tractor bed assemblies. These options all have significant disadvantages. For example, for vertical-type casks, heavy multi axle specialized carrier trailers require an extended operating space and are not capable of engaging and moving the casks out of the fuel building(s), or of doing the actual positioning the cask in the close spacing requirements within the ISFSI. Removing the cask from the fuel building typically requires some type floor level transfer capability such as industrial air cushion devices (air bearings), heavy capacity roller devices, or in-floor rails with low profile transfer cars. At the ISFSI, final spacing is accomplished by transferring the casks from the trailers by using industrial air cushion devices (air bearings) or heavy capacity roller devices. Furthermore, a disadvantage of air cushion devices is that they require a large pressurized air supply and a smooth, non-porous surface in order to maintain lift and operate properly. Moreover, specialized vertical lift gantry frames attached to crawler tractor bed assemblies have the disadvantage of a large size, especially height, and a lack of maneuverability. The crawler treads tend damage operating surfaces when skid turning under these types of loading conditions.
Another option for horizontal type spent nuclear fuel casks are In Plant-Self-Propelled Modular Transporters (IP-SPMT). An IP-SPMT refers to a low-profile deck, multi-axle, self-propelled transporter, with all-wheel drive independent suspension axle assemblies that are typically used in combinations to carry loads heavier than 80 tons. An IP-SPMT is typically internal combustion engine-electric powered and has six to twelve or more on-center rotation axle assemblies. The axles can be independently steered by varying each wheel motor speed and direction.
However, in vertical-type spent nuclear fuel cask applications, existing IP-SPMT devices are not sufficient because of the need to pick and place the vertical cask directly to or from the operating surface. One IP-SPMT device proposed by the inventor of the present application utilizes uniload axle assemblies as disclosed in U.S. Pat. No. 5,379,842, wherein the axles assemblies are gear motor rotated for steering coupled with hydraulic differentially power driven wheels. Referring to FIG. 4, the uniload axle assembly 106 includes a drive motor 14 having mounted thereon a pinion gear 16 in mesh with a ring gear 18 which is bolted to a circular plate as explained hereinafter. The drive motor 14 is bolted to a piston top plate to which is secured a square machined upper shaft 26 to transmit the torque from the top plate to the wheel set via a square torque plate upper flange 28 which is sectional so that it may be removed. A pair of wheels 34 are mounted to axles which form a relatively fixed part of wheel truck 38 which includes a yoke portion. Trunnions 42 are mounted on the sides of the bottom casing which houses a piston secured to the upper shaft 26. Ongoing design versions of the same patent concept eliminate the gear motor steering for differential steering where all-wheels are electrically driven with computer controlled differential steering.
Although the uniload axle assembly 106 disclosed in U.S. Pat. No. 5,379,842 addresses the problem in the conventional art overloading operating surfaces, the disclosed uniload axle assembly 106 has a foot print too large for some applications, including vertical cask transportation.
Accordingly, what is needed is a heavy capacity self-loading transporter with an on-center rotation independent axle assembly that is devoid of scrubbing action while turning under full load so that casks can be moved from nuclear refueling facilities having narrow entry ports and restricted door heights to an ISFSI.